The invention relates to a solenoid valve.
Solenoid valves of this type are used e.g. as pressure-limiting valves in hydraulic circuits orxe2x80x94more recentxe2x80x94in the control of common-rail diesel injection systems. Such valves are characterized by good response, which makes possible a fast pressure reduction in the system, e.g. in the common rail. In design, an effort has been made to structure the valves so that they are as compact as possible, while the flow resistance should be as low as possible.
A previous solenoid valve in flat armature construction is described in DE 43 05 789 A1, in which a coil form is held in an iron corexe2x80x94called the housing in the following. When the coil winding is not under load, the armature forms an axial slot with a pole core. In the known solution, a plunger is fastened to the flat armature, the free end section of which forms a spherical valve body against a valve seat when it is in base position.
To decrease the manufacturing technology expense in manufacturing the housing, the pole core and the part of the housing that holds the coil form can be designed as two partsxe2x80x94as suggested in DE-OS 31 26 246. In designs such as this, the pole core stressed on its face that is at a distance from the flat armature with the fluid pressure acting on the valve body, so that a resulting pressure force acting in axial direction acts on the pole core. Since the pole core is often mounted by being pressed into the housing, under unfavorable conditions, i.e. with high input pressure and insufficient contact pressure between pole core and housing, it is possible for the pole core to be slid in axial direction toward the flat armature. Because of this change in the air gap, the magnetic force acting on the flat armature can no longer be unambiguously correlated to the opening cross section of the valve seat. This can lead to the fact that the valve response no longer corresponds to the specifications so that recalibration of the solenoid valve is necessary.
In contrast, the present invention is based on the task of producing a solenoid valve in which functional safety is improved with minimum equipment technology expense.
The task is solved by the characteristics of a solenoid valve according to the present invention.
When the solenoid valve shown in FIG. 1 has power supplied to it, the armature 38 is stressed with a force. This axial force is transferred over the armature 38 to the plunger 36 so that its tip presses the valve body 28 against the valve seat 34 and thus the pressure on the input connection P can be varied.
Because of the measure according to the invention of stressing the pole core, which is separate from the housing, axially with about the same pressure, even a high input pressure can not lead to the pole core becoming displaced and the air gap thereby becoming changed. In this way, taking special measurements for axial determination in the housing can be avoided so assembly can be carried out in the previously customary manner, e.g. by pressing or crimping.
Since the input connection is frequently connected to a drain or tank connection by way of the pressure limiting valve, it is especially advantageous if this low system pressure (tank pressure) is applied to both faces of the pole core.
In a preferred variation, the housing is provided with a ring-shaped pole disk, whose side turned toward the armature matches the adjacent face of the pole core so that the axial air gap is limited on side by the armature and on the other side by the pole core and the pole disk.
It is especially simple to manufacture the solenoid valve according to the invention if the pole disk is crimped with the housing.
Usually a plunger is fastened on the flat armature, this plunger acting on the valve body with its free end section and pressing it against the valve seat in basic position (minimum air gap). In this process, the plunger passes through the pole core along its axial direction. In a first alternative, a compensating channel can be formed to produce the pressure compensation between the two pole core faces, in that the plunger cross section is designed with a smaller dimension or with flattened areas, etc. so that a compensating channel is formed between the axial hole of the pole core and the plunger. Alternatively to this, a corresponding channel can be formed on the outer circumference of the pole core so that this compensation channel is delimited by the housing and the outer circumference of the pole core. In both variations, it is insured that the face on the valve seat side and the face on the armature chamber side of the pole core can be stressed with the same pressure with minimum manufacturing technology effort.
This effort can be further reduced if the valve seat is formed on an insert piece that is installed in the housing. In this process, the connection is preferably made by crimping.
In this design, the chamber of the housing formed upstream of the insert piece is connected to the holding chamber for the pole core by way of a connecting hole. In this, the connecting hole is designed so that it is larger than the corresponding outer diameter of the plunger passing through it so that the ring chamber between plunger and connecting hole is part of the compensating channel for stressing the two pole core faces with pressure.
The armature chamber of the housing is preferably closed with a cover that has coil pins passing through it, while sealing rings are provided for the coil pins in the feed-through hole.
The structure of the valve is especially simple if this cover is designed as a connector or pin exit.
In this process, it is especially preferred if the housing is chamfered along some of its circumference for fastening the cover.
Other advantageous further developments of the invention will be apparent from the description and claims that follow hereinafter.